The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        CSI channel state information        CQI channel quality indicator        DL downlink        eNB/eNodeB node B/base station in an E-UTRAN system        E-UTRAN evolved UTRAN (LTE)        LTE long term evolution (E-UTRAN)        LTE-A long term evolution-advanced (of E-UTRAN)        PDCCH physical downlink control channel        E-PDCCH enhanced physical downlink control channel        PDSCH physical downlink shared channel        PUSCH physical uplink shared channel        RF radio frequency        SINR signal to interference plus noise ratio        UE user equipment        UL uplink        UTRAN universal terrestrial radio access network        
In conventional LTE, the network allocates uplink PUSCH and downlink PDSCH radio resources to its various UEs by means of a PDCCH. Each UE attempts to decode at least part of the PDCCH to see if the UE identifier is listed there; if yes the UE decodes further to find its resource allocation(s) and if no the UE can disregard that PDCCH. This is known as blind decoding since the UE does not know in advance whether any given PDCCH is addressed to it. Among all the UEs in a cell the PDCCHs are distributed, so that different groups of UEs look for a PDCCH addressed to them in different time intervals. This also allows the UEs to go into a sleep or low-power mode between their scheduled PDCCH time intervals, so long as they have no ongoing data processes, by a mechanism termed in the art as a discontinuous reception cycle. The PDCCHs in a cell are therefore transmitted in a distributed manner. Since the PDCCHs are distributed across the whole spectrum (or across the whole component carrier for the case of a carrier aggregation system such as LTE-A), the UE's PDCCH search space is the whole control channel region of the whole bandwidth (or of the component carrier bandwidth) for the duration of its assigned PDCCH time interval.
In the ongoing standardization of the LTE-A system there is an enhanced PDCCH (E-PDCCH) which is based on localized radio resources. The E-PDCCH has the potential to improve the efficiency of the conventional PDCCH by using beamforming and multiple-antenna techniques, though exactly how the E-PDCCH is to operate is at this time far from settled. Certain proposals envision the E-PDCCH as being time or frequency division multiplexed with resource elements (or even with OFDM symbols) within the PDSCH region of the bandwidth. Others propose a hybrid time/frequency division such as is used for the relay PDCCH R-PDCCH. See for example US Patent Application No. 20110044391 entitled “Plural Channels for Transmission of a Single Pulse Train”, and US Patent Application No. 20110170496 entitled “Channel Assignment” for details as to the E-PDCCH being disposed in the data (PDSCH/PUSCH) region of the bandwidth.
Still there remain some essential unresolved issues concerning the E-PDCCH. Specifically, it is not yet determined what criteria the eNB will use to choose between using a PDCCH or an E-PDCCH for scheduling any specific UE, nor is it settled where in frequency the eNB should put the E-PDCCH if that's the chosen scheduling mechanism. Embodiments of these teachings resolve these open issues in a manner that is particularly advantageous from the UE's power-limited perspective.